The Minnesota Twin Family Study (MTFS) seeks to identify genetic and environmental influences on alcohol abuse and associated psychological disorders. An epidemiologically based sample of 600 female adolescent twins and their parents (a total of 2400 individuals) will undergo a one-day comprehensive assessment that includes assessment of (1) mental health, (2) substance use and abuse history, (3) psychophysiological markers of risk, (4) personality/interests/social adjustment, and (5) environmental potentiators of risk. Two cohorts will be assessed: half the twins will be assessed when they are 11 years old, just prior to their initial experimentation with alcohol and other drugs, and half the sample will be assessed at age 17, prior to the establishment of adult drinking patterns and the onset of adult psychological disorders. The sample will be selected in such a way that an expected 40% of the twins will have one or both biological parents with a DSM-III-R diagnosis of Alcohol Dependence (i.e., High Risk), an expected 20% of twins will have one or both biological parents with a DSM-III-R diagnosis of Alcohol Abuse but not Alcohol Dependence (i.e., Medium Risk), an expected 10% will have one or both biological parents with a psychiatric disorder but not a substance abuse diagnosis (i.e., Psychiatric Controls), and an expected 30% of twins will have both biological parents with no psychiatric or substance abuse diagnosis (i.e., Controls). The project is designed to be a prospective study of the etiology of alcoholism and related disorders: the hope is that the sample will be reassessed every three years as the twins progress through the major life changes that characterize adolescence and early adulthood. The focus of analysis of first wave assessment data will be on the high-risk aspects of the design as well as on understanding adolescent alcohol use and abuse from a behavioral genetic perspective. That is, we will seek to (1) identify early markers of risk, (2) characterize the genetic and environmental determinants of individual differences in these markers, and (3) identify interactions between biological risk status and environmental factors. Additionally, the proposed study of female adolescent twins parallels an ongoing study of 600 male adolescent twins and their parents. This will provide us with the unique opportunity to identify sex differences in the origins of alcoholism and related disorders, and determine whether and how those sex differences interact with genetic and environmental markers of risk.